A variety of portable electronic devices, such as cellular phones, smartphones, and multimedia devices, include display controllers (display drivers) to control the display of graphics and other images on display panels of the devices. Additionally, such electronic devices are typically configured to operate in either a full power mode or a reduced power mode (e.g., standby or sleep mode) at appropriate times. For instance, the devices are generally configured to operate in reduced power modes to conserve battery power during time periods when the devices are powered on, but are not being actively used by their users. A power management system of an electronic device may place the device in reduced power mode either automatically (e.g., after detecting that the device has not been used by a user for a period of time) or in response to manual activation of the reduced power mode by a user of the device, such as when the user knows that the device will not be actively used for a while.
In full power mode, an electronic device typically executes one or more applications that generate graphics or other images for display on the device's display panel. Each application sends image information to a graphics processor of the electronic device to produce display data for use by the display controller. The display controller then processes the display data to provide it in the proper format to the display panel.
By contrast, in reduced power mode, many portable electronic devices deactivate their display controllers (or at least portions thereof) so as not to display anything on their display panels. While such an approach saves precious battery power, it also leaves the device user in the dark, with no indication of whether the electronic device is on and no provision of even minimal information which may be of interest to the user, such as time of day, battery state of charge, signal strength, and so forth.
A partial electrical block diagram of an exemplary prior art electronic device (e.g., a smartphone) 100 having display capability is illustrated in FIG. 1. The device 100 includes an application processor 101, a display controller 103, a display panel 105, a power management integrated circuit (IC) 107, and an oscillator 109 for use in establishing a clock signal for the electronic device 100. The application processor 101 includes a graphics processor 111 that produces display data for graphics and other images to be displayed in accordance with the requirements of the applications being executed by the applications processor 101. The display controller 103 (or, equivalently, display driver) typically includes an input interface 113, an incoming data processor 115, memory 117 for storing incoming display data, an output data processor 119, an output data buffer 121, a power management circuit 123, and a display system oscillator and phase locked loop (PLL) 125 to supply a timing reference for the display controller 103. The power management IC 107 typically includes a real time clock 127 that receives its timing reference from the oscillator 109. The real time clock 127 is typically used to provide a clock signal for the application processor 101 and various other digital components of the electronic device 100.
In operation, the application processor 101 executes applications that require display of certain images, such as graphics, photographs, and/or text. The display data for the images is generated by the graphics processor 111 and supplied to the display controller 103 via the input interface 113. The incoming data processor 115 processes the received display data and stores the display data in the display controller memory 117. The output data processor 119 retrieves the display data from the memory 117 in accordance with the frame rate and other display format parameters of the display panel 105 and directs the retrieved display data into appropriate locations of the data output buffer 121 for display on the display panel 105.
When the power management IC 107 detects a power management condition, such as expiration of an inactivity timer or receipt of a user input requesting that the electronic device 100 be placed into reduced power mode (e.g., standby or sleep mode), the power management IC 107 sends a control signal or command to the power management circuit 123 of the display controller 103. Upon receipt of the command from the power management IC 107, the display controller's power management circuit 123 sends a signal to the output data processor 119 instructing the output data processor 119 to stop supplying data to the data output buffer 121 for display on the display panel 105. The result of the power management processing is that the display panel 105 and part of the display controller 103 are deactivated. As discussed above, deactivating the display panel 105 and/or display controller 103 saves battery power, but it leaves the device user with no indication of whether the electronic device 100 is on and no provision of even minimal information which may be of interest to the user.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements to help improve the understanding of the various exemplary embodiments of the present invention.